Duane writes:
> * There is a big issue with mpe applications
>   with regard to the file system. In mpe you
>   have files that can be different types and
>   based on the type you get different/specialized
>   behavior. Emulating this on Linux with little
>   or no source code change might be a challenge.
>   But, Linux does support different file systems
>   so an enterprising individual could implement
>   a complete mpe file system.

And someone wrote to me privately:
> So now I wonder, does it buy anything to write an MPE file system (with
> entry points to implement the Linux Virtual File System) or can you
> piggy-back on ext3 and add the MPE file labels, record oriented access,
> etc.?

The big problem is that once you have it working for "MPE", it probably
won't work very well for Unix anymore.  One of the first laws of Unix is
that everything is just a stream of bytes, and everything in the system
orbits around that idea.  As soon as you introduce MPE-style files, you'll
find that nothing in the Unix world will know how to deal with them in all
cases (no matter how clever your file system is, and I can think of a lot of
really clever ideas in this area).

This is one of the failings of MPE, that files have such a complex interface
that it is very hard to write general purpose programs without a huge amount
of conditional code to handle all possible cases.

Also you can expect the Unix/Linux world to think that the whole idea is
just one massive perversion, so any hope of getting an MPE file system into
the Linux kernel, say, will have an uphill battle at best.

Having said that, we've done a fair amount of design work in this area
(enough to decide on what we think are the best ways of doing most things)
and I know other developers are working on (and some have deployed) various
degrees of MPE file system compatibility on Unix.

But the simplest and most straightforward or "obvious" ways of doing
compatibility tools for MPE-on-Unix may not be as desirable as they seem.

The trick in any migration is to avoid simply ending up as a "refugee".  A
refugee is someone who lives in a foreign land, against their will, often in
a tent on the periphery of the local society, speaking a different language,
ignored (and perhaps despised) by the local population, etc.  Just because
you have some sort of "MPE file system" and a collection of other tools that
let you pretend to be MPE on Unix, you're always just going to be
"pretending", and the question is whether this is really a viable result or
whether you're just going to continue to suffer all the problems of an
obscure proprietary system (can't hire people who understand it, etc.).

These are the issues that we are working on at the moment.  The goal is to
give MPE users a brighter future than "refugee status" or having to throw it
all away and start all over.  I think we can do it.

G.

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